The present invention relates to gas sensors. More particularly, the present invention relates to an exhaust gas sensor.
Exhaust sensors are used in a variety of applications that require qualitative and quantitative analysis of gases. For example, exhaust sensors have been used for many years in automotive vehicles to sense the presence of exhaust gases. In automotive applications, the direct relationship between various exhaust gas concentrations and the air-to-fuel ratios of the fuel mixture supplied to the engine allows the sensor to provide concentration measurements for determination of optimum combustion conditions, maximization of fuel economy, and the management of exhaust emissions. The management of exhaust emissions has become increasingly important because of the increased use of automobile engines.
One method of sensing exhaust gas uses electrochemistry. With an electrochemical method, there are two basic principles involved in gas sensing: the Nernst principle and the polarographic principle. Typically, an exhaust gas sensor utilizing an electrochemical method comprises an electrochemical pump cell (polarographic principle) and an electrochemical motive force cell (Nernst principle).
With the Nernst principle, chemical energy is converted into electromotive force (xe2x80x9cemfxe2x80x9d). A gas sensor based upon this principle typically consists of an ionically conductive solid electrolyte material, a porous electrode with a porous protective overcoat exposed to exhaust gases (xe2x80x9csensing electrodexe2x80x9d), and a porous electrode exposed to a known gas""s partial pressure (xe2x80x9creference gas electrodexe2x80x9d). Sensors typically used in automotive applications use a yttria stabilized zirconia based electrochemical galvanic cell with porous platinum electrodes, operating in Nernst mode, to detect the relative amounts of a particular gas, such as oxygen for example, that is present in an automobile engine""s exhaust. Also, a typical sensor has a ceramic heater attached to help maintain the sensor""s ionic conductivity. When opposite surfaces of the galvanic cell are exposed to different oxygen partial pressures, an electromotive force is developed between the electrodes on the opposite surfaces of the zirconia wall, according to the Nernst equation:       E    =                  (                              -            RT                                4            ⁢            F                          )            ⁢              ln        ⁡                  (                                    P                              O                2                            ref                                      P                              O                2                                              )                          where    :          
        ⁢                                        "AutoLeftMatch"                          E              =                              xe2x80x83                            ⁢                              electromotive                ⁢                                                      xe2x80x83                                    ⁢                                      xe2x80x83                                                  ⁢                force                                                                                      R            =                          xe2x80x83                        ⁢                          universal              ⁢                              xe2x80x83                            ⁢              gas              ⁢                              xe2x80x83                            ⁢              constant                                                                        F            =                          xe2x80x83                        ⁢                          Faraday              ⁢                              xe2x80x83                            ⁢              constant                                                                        T            =                          xe2x80x83                        ⁢                          absolute              ⁢                              xe2x80x83                            ⁢              temperature              ⁢                                                xe2x80x83                                ⁢                                  xe2x80x83                                            ⁢              of              ⁢                                                xe2x80x83                                ⁢                                  xe2x80x83                                            ⁢              the              ⁢                                                xe2x80x83                                ⁢                                  xe2x80x83                                            ⁢              gas                                                                                      P                              O                2                            ref                        =                          xe2x80x83                        ⁢                                          oxygen  partial  pressure
of  the  reference  gas                                                                                                    P                              O                2                                      =                          xe2x80x83                        ⁢                          oxygen  partial  pressure
of  the  exhaust  gas                                          
With the polarographic principle, the sensors utilize electrolysis whereby ions are sensed through a diffusion limiting current for aqueous electrolyte systems. The same approach can be applied to solid electrolyte systems for sensing gas species and for sensing of wide range air-to-fuel ratio of combustion exhaust gas systems. Generally, a sensor employing the polarographic principle is composed of a pair of current pumping electrodes where both are in contact with an oxide conductive, solid electrolyte and one electrode is in contact with a gas diffusion limiting means. The gas diffusion limiting means in conjunction with the pump electrodes create a limiting current which is linearly proportional to the measured gas concentration in the sample.
A known type of exhaust sensor includes a flat plate sensor formed of various layers of ceramic and electrolyte materials laminated and sintered together with electrical circuit and sensor traces placed between the layers in a known manner. In this sensor, the sensing element can be both difficult and expensive to package within the body of the exhaust sensor since it generally has one dimension that is very thin and is usually made of brittle materials. Consequently, great care and time consuming effort must be taken to prevent the flat plate sensing element from being damaged by exhaust, heat, impact, vibration, the environment, etc. This is particularly problematic since most materials conventionally used as sensing element supports, glass and ceramics for example, cannot withstand much bending. With the use of ceramic materials, thermal shock resistance is a primary concern. This has an effect of influencing sensor manufacture because of the precautions taken to preserve during the sensor""s lifetime the fragile ceramic materials, i.e., to prevent cracking from thermal shocks, and the sensor""s electronics for heating control and sensing.
Accordingly, there remains a need in the art for a sensor that is durable and that can be fabricated easier and at a reduced cost.
The deficiencies of the above-discussed prior art are overcome or alleviated by the gas sensor and method of producing the same.
A gas sensor is disclosed comprising an oxygen pump cell having at least one exterior pump electrode and at least one interior pump electrode disposed on opposite sides of a first solid electrolyte layer. An emf cell having a first and second emf electrodes and first and second reference gas electrodes are disposed on opposite sides of a second solid electrolyte layer. At least one insulating layer is in contact with the first and second emf electrodes. At least one via hole is disposed through the first solid electrolyte layer. At least one air channel is disposed through at least one insulating layer. An air vent is disposed in at least one insulating layer in contact with the first and second reference gas electrodes. A heater is disposed in thermal communication with the sensor. And at least five electrical leads are in electrical communication with said sensor.
A method of using a gas sensor is disclosed comprising measuring a first emf value between the first emf electrode and the first reference gas electrode. Comparing the first emf value with a first pre-determined voltage value for driving a first pump current between the first exterior pump electrode and the first interior pump electrode. Measuring a second emf value between the second emf electrode and the second reference gas electrode. Comparing the second emf value with a second pre-determined voltage value for driving a second pump current between the second exterior pump electrode and the second interior pump electrode. Determining concentrations of gases by comparing values between the first emf electrode and the second emf electrode. Measuring the first pump current and the second pump current between the first exterior pump electrode and the first interior pump electrode.
A method of using a gas sensor is disclosed comprising measuring a first emf value between the first emf electrode and the first reference gas electrode. Comparing the first emf value with a first pre-determined voltage value for driving a pump current between the exterior pump electrode and the interior pump electrode. Measuring a second emf value between the second emf electrode and the second reference gas electrode. Comparing the second emf value with a second pre-determined voltage value. Determining concentrations of gases by comparing emf value between the first emf electrode and the second emf electrode. Measuring the pump current between the exterior pump electrode and the interior pump electrode.